1. Field of the Invention
The present invention relates to a method for making improved rocker panels and rocker panels made thereby.
2. Description of the Prior Art
A variety of injection molded parts are made and used for automobile body and trim parts. For example, bumpers, spoilers, body panels, doors, filler panels, wheel covers, dashboards, armrests, and other parts are commonly made by injection molding of thermoplastic materials. In addition, side sill garnishes, rocker panels, and rocker molds may be made by the injection molding process.
These plastic parts often have attachment means on their back or hidden sides in order to affix them to or mount them on an automobile. A common method of attaching plastic parts to automotive vehicles involves providing a plurality of clip houses on the backside of the plastic part. The clip houses are often molded on the backside of the part simultaneously with the molding of the part itself. The clip houses generally provide stand off surfaces to which mounting clips are attached. The plastic part may then be mounted on the automobile by aligning the mounting clips with corresponding holes or openings in the automobile, and pressing the plastic part into position. The mounting clips thereby exert a force to positively retain the plastic part against the automobile.
Plastic parts such as rocker panels, and the like, usually must withstand greater environmental stresses than other plastic parts. Rocker panels and side sill garnishes, for example, are usually attached to an automobile body below the door opening. Because of this position, these parts are subject to being stepped on by occupants entering and exiting the vehicle, road vibration, and being struck by foreign objects and debris. Thus, plastic parts intended for these applications require significantly stronger means for attaching them to the automobiles. One common method for providing stronger clip house mounting structures is to significantly thicken the legs of the clip house. However, as injection molded plastic cures, it tends to shrink. Where the clip house leg is joined to the backside of a plastic part, the observable effects of plastic shrinkage become more pronounced. The result is the appearance of a sink mark or line on the front surface of the plastic part opposite the attachment point for the clip house leg. As the clip house leg is thickened to provide additional support, the appearance of sink marks or lines becomes more pronounced. In plastic parts where an aesthetically pleasing external appearance is desired, the appearance of sink marks or lines is undesirable.
This is especially true where plastic parts are provided with a painted or other decorative surface such as by means of film lamination techniques. In such, film lamination techniques, a paint film laminate is co-molded over an external show face surface of the plastic part. The film laminate is typically pre-formed, inserted into a mold cavity, and a thermoplastic resin is injected under pressure into the mold cavity against the backside of the laminate. The result is a plastic part having a film laminate co-molded over a plastic substrate. Laminated paint films are detailed in U.S. Pat. No. 5,514,427, the entire disclosure of which is incorporated by reference herein. Techniques for preforming paint film laminates and insert molding film-plastic parts are disclosed in U.S. Pat. No. 5,599,608, the disclosure of which is incorporated herein by reference.
An additional problem with prior art methods of strengthening clip house attachment structures on plastic parts by thickening the support legs of the clip house structures is that they do not provide additional flexural rigidity to the plastic part. For example, many plastic parts, such as side sill garnishes and rocker panels, have substantial portions which are not supported along their back surfaces. These unsupported portions are subject to greater flexural deflections than adjoining supported portions. Repeated excessive flexing of the plastic parts can lead to the dulling of glossy finishes or the formation of visible cracks in external show face surfaces of the parts and may ultimately lead to fatigue and mechanical breakdown of the parts.
Accordingly, there remains a need in the art to improve the existing methods for strengthening attachment structures on the backsides of plastic parts for automobiles so as to prevent the formation of sink marks or lines on show face surfaces of the plastic parts.
Also, there remains a need in the art to improve the existing methods for reinforcing plastic parts for automobiles so as to provide for greater resistance to excessive flexing of the parts.